JP4193251B2 - Resin tube - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a cylinder formed by injection molding.
[0002]
[Prior art]
The applicant of the present application has previously filed an invention in which the lead holding member of the mechanical pencil is formed as a resin cylinder and the cylinder is installed in a core protection tube disposed at the tip of the mechanical pencil. (Japanese Patent Laid-Open No. 9-183294).
[0003]
According to the invention, since the lead holding member is disposed at the tip of the mechanical pencil, the lead can be used as effectively as possible without waste, but there is still room for development.
[0004]
[Problems to be solved by the invention]
This is a problem of the productivity of the cylinder that is the core holding member. Although this cylindrical body is formed by injection molding, the cylindrical body adheres to the core pin, and it is extremely difficult to remove the extremely small cylindrical body from the core pin. Incidentally, the cylinder has a length of about 5 mm, a diameter of about 1 mm, and an inner diameter of about 0.5 mm.
Here, generally, several tens to several hundreds of cylinders are formed at a time. This is a so-called “manufacturing” method. For this reason, the interval between the core pins is narrow, and therefore, if the cylinder is firmly attached to the core pin located in the middle, the difficulty of removing it is significantly improved.
Therefore, it has been considered to attach an extrusion plate 103 for ejecting the core holding member (molded product) 102 to the core pin 101. However, not only the mold apparatus is enlarged, but the molded product is small because it is small. If it is compressed or somewhat, it may be cramped (see FIG. 8), which is not realistic.
[0005]
[Means for Solving the Problems]
The present invention has been made in view of the above problems, and is a cylinder formed by injection molding, and the surface roughness of the inner surface of the cylinder is made rougher than the surface roughness of the outer surface. The inner surface of the cylinder is formed by a core pin blasted with particles of Nos . 100 to 400 ,
The gist is that the cylindrical body is a mechanical pencil core holding member.
[0006]
[Action]
The minute irregularities on the inner surface of the molded product slide on the minute irregularities on the surface of the core pin and come out of the core pin, and then the molded product left in the cavity contracts.
[0007]
【Example】
A first example will be described with reference to FIGS. A core tank 2 for storing a plurality of cores is disposed inside the shaft cylinder 1 so as to be movable back and forth. An eraser 3 and a knock cap 4 are detachably attached to the rear end of the core tank 2.
On the other hand, a chuck body 6 that holds and releases the lead via a relay member 5 is fixed in front of the lead tank 2. A chuck ring 7 for opening and closing the chuck body 6 surrounds the front portion of the chuck body 6. Reference numeral 8 denotes a tip member screwed into the tip of the shaft tube 1. A lead detent member 9 for preventing the lead from returning is press-fitted and fixed inside the tip member 8. It is not necessary. Reference numeral 10 denotes an elastic member such as a coil spring, which urges the chuck body 6 backward together with the core tank 2.
[0008]
A core protecting tube 11 made of a metal pipe is press-fitted and fixed to the front end of the tip member 8, but may be integrally formed with the tip member 8 by, for example, injection molding, or a separate member. However, it may be formed integrally with the tip member by insert molding or the like.
A cylindrical core holding member 12 formed by injection molding is disposed inside the core protection tube 11. Further, before and after the core holding member 12, fixing rings 13 and 14 that prevent the core protection tube 11 from falling off are press-fitted into the core protection tube 11. Of course, the inner diameter of the fixing rings 13 and 14 is larger than the diameter of the core used.
As a method for preventing the core holding member 12 from falling off, the inner member 8a may be formed in the tip member 8 and the fixing ring 14 may be press-fitted forward (see FIG. 3). It may be possible to prevent the core protection tube 11 from falling off by forming a step on the front inner surface.
[0009]
Here, the core holding member 12 will be described in detail. The outer diameter of the core holding member 12 is formed to be substantially the same as or slightly larger than the inner diameter of the core protection tube 11. On the other hand, the inner diameter of the core holding member 12 is slightly smaller than the outer diameter of the core to be used. Therefore, when the core is inserted into the core holding member 12, the core holding member 12 is compressed by its own elasticity, clamps the core by its reaction force, escapes outward, and presses against the inner surface of the core protection tube 11. By these actions, rotation of the core with respect to the core holding member 12 and rotation of the core holding member 12 with respect to the core protection tube 11 are prevented, and thus rotation of the core (remaining core) away from the chuck body 6 is prevented. In other words, it is possible to write without any discomfort even in the remaining core.
[0010]
Further, the inner surface and the outer surface of both ends of the core holding member 12 are chamfered. The inner surface chamfered portion 15 is provided to facilitate guiding the core to the core holding member 12, while the outer surface chamfered portion 16 is provided to facilitate assembly of the core holding member 12 to the core protection tube 11. .
Furthermore, the surface roughness of the inner surface of the core holding member 12 is formed to be rougher than the surface roughness of the outer surface. This is also in consideration of productivity at the time of molding, which will be described later. In addition, by forming the inner surface of the core holding member 12 in contact with the core roughly, the roughness of the surface of the core matches the surface roughness of the inner surface of the core holding member. The effect of preventing the rotation of the core with respect to the core holding member is further increased.
[0011]
Examples of the material for the core holding member include silicone rubber and acrylonitrile-butadiene rubber. The core holding member is formed of a crystalline resin, for example, a mixed material containing polypropylene or polyethylene, or a crystalline resin alone. Is a suitable example. It is a substance having a high shrinkage ratio of the molded product after injection molding, which will be described later, and thus having good detachability from the cavity.
[0012]
Next, a method for forming the core holding member 12 will be described. Reference numeral 17 denotes a cavity plate in which a cavity 18 in which a core holding member (molded product) is formed is formed. A core pin 19 that forms a through hole in the core holding member jumps into the cavity 18. On the surface of the core pin 19, fine irregularities are formed for forming minute irregularities on the inner surface of the core holding member to be molded. Specifically, the surface of the core pin 19 is blasted with about 100 to 400 particles. On the other hand, the inner surface of the cavity 18 in which the outer surface of the core holding member is formed is not subjected to a roughening process such as blasting, and therefore the outer surface of the core holding member to be molded has a substantially smooth surface. It has become.
[0013]
Next, the operation will be described. First, the resin is poured into the cavity from the state of FIG. 4 to perform injection molding. Next, the cavity 18 and the core pin 19 are separated from each other. At this time, the molded product (core holding member 12) becomes the core pin due to the minute unevenness of the core pin 19 and by the sticking action of the molded product to the cavity. And remains in the cavity 18 (see FIG. 5).
Here, the molded product in the cavity shrinks as it cools with time, and at this point, it is easy to separate (peel) from the cavity. Finally, air or the like is blown onto the cavity, and the core holding member (molded product) is discharged from the cavity. Although the outer surface of the core holding member obtained by this injection molding is a smooth surface (only a slight amount is formed with fine irregularities: see FIG. 6), the inner surface is shown in FIG. As shown, the density of minute irregularities is increased. That is, the inner surface of the core holding member is rougher than the outer surface.
[0014]
【The invention's effect】
According to the present invention, a small cylindrical body can be easily formed and produced without difficulty.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view showing a first example.
FIG. 2 is an enlarged view of a main part of FIG.
FIG. 3 is an enlarged view of a main part showing another example of a fixing method of the core holding member.
FIG. 4 is a cross-sectional view of a main part at the start of injection molding.
FIG. 5 is a cross-sectional view of a main part at the time of completion of injection molding.
FIG. 6 is an enlarged external view of the outer surface of the core holding member.
FIG. 7 is an enlarged external view of the inner surface of the core holding member.
FIG. 8 is a cross-sectional view of a main part showing a conventional injection molding method.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Shaft cylinder 2 Core tank 3 Eraser 4 Knock cap 5 Relay member 6 Chuck body 7 Chuck ring 8 Tip member 9 Core detent member 10 Rebound member 11 Core protection tube 12 Core holding member 13 Fixed ring 14 Fixed ring 15 Inner surface chamfer 16 Chamfered portion 17 Cavity plate 18 Cavity 19 Core pin

Claims (1)

A cylinder formed by injection molding, the inner surface of the cylinder is made to have a surface roughness that is greater than the surface roughness of the outer surface, and the inner surface of the cylinder is blasted with particles 100 to 400 A resin cylinder formed by a core pin, wherein the cylinder is a mechanical pencil core holding member.

Images